State of the art waterjet propulsors for marine craft utilize an impeller that pressurizes water supplied to the impeller from a water inlet. The pressurized water than passes through a stator that has fixed vanes to straighten out the water flow exiting the impeller. After exiting the stator, the pressurized water passes through a water-accelerating nozzle to thereby generate propulsive thrust. This type of waterjet propulsor is called a pressurized system waterjet here.
A shortcoming of these existing pressurized system waterjet designs is that they suffer serious performance falloff when air or other gas is included in their inlet fluid flow. Tests run on pressurized system waterjets at Pratt and Whitney Aircraft in the sixties showed that serious loss of performance resulted from as little as three to five percent of air or other gases by volume of total inlet fluid flow. This is because the compressible gas degrades the efficiency of the waterjet""s water pressurizing impeller. Two primary sources of air entrained in the inlet water of a waterjet are due to: 1) Boats operating in rough seas where air flow is trapped under the hull and passes into the waterjet inlet and 2) Air cushioned boats where the underside of the hulls are partially aerated as a normal condition of operation.
As a point of interest, some of Applicant""s earlier work, such as given in the continuation-in-part applications listed under a preceding section titled CROSS REFERENCE TO OTHER APPLICATIONS, revolve around enclosed or semi-enclosed rotor propulsors that operate partially aerated as a preferred condition. Such units are designed to operate as mainly non-pressurized systems with their rotors aerated. As such, it is normally not necessary to bleed off entrained air or gas in their water inlets.
A second shortcoming of existing waterjets is that, in boats with multiple waterjet propulsors, the drag or resistance of a non-operating waterjet becomes very high as boat speed is increased. This is due to the resistance of the water flow passing through the non-operating waterjet.
The instant invention addresses both of the aforementioned shortcomings of existing state-of-the-art pressurized system waterjets. This is accomplished by offering a way to bleed off part or all of the air in the waterjet inlet water and a way to deflect at least most of the water from entering the inlet of a non-operating waterjet when moving forward a high speeds. A further enhancement is the use of air fences that restrict water containing entrained air from entering from the sides of the waterjet""s water inlet. For purposes of this application, high speed is defined as being fifteen knots or higher.
With the foregoing in mind, it is a principal object of the present invention to provide an improved waterjet propulsor for marine craft that has a boundary layer bleed opening disposed, at least in its majority, forward of the waterjet propulsor""s powered rotor, said boundary layer bleed opening taking in aerated boundary layer water thereby reducing the amount of air entering the powered rotor during high speed forward operation of the marine craft.
A related object of the invention is that the boundary layer bleed opening extends, as a sum of its openings, over a majority of a width of the waterjet""s fluid inlet.
A further object of the invention is that aerated boundary layer water taken in by the inlet boundary layer bleed opening passes through a valve that controls flow of the aerated boundary layer water.
Yet another object of the invention is that the aerated boundary layer water taken in by the inlet boundary layer bleed opening passes through a bypass pump that accelerates flow of the aerated boundary layer water.
Another related object of the invention is that at least a portion of the aerated boundary layer water taken in by the inlet boundary layer bleed opening be dispensed or discharged into the waterjet propulsor downstream of the waterjet rotor.
A directly related object of the invention is that at least a portion of the aerated boundary layer water taken in by the boundary layer bleed opening be dispensed or discharged from a stator vane assembly disposed downstream of the waterjet rotor.
Another related object of the invention is that at least a portion of the aerated boundary layer water taken in by the boundary layer bleed opening be dispensed or discharged from a waterjet nozzle of the improved waterjet propulsor.
A further object of the invention is that there be a first air fence disposed, at least in its majority, to one side of the waterjet fluid inlet.
A directly related object of the invention is that there be a second air fence disposed, at least in its majority, to an opposite side of the waterjet fluid inlet from the first air fence.
Yet another object of the invention is that it include an inlet flow deflector that, when extended, deflects fluid flow from entering the waterjet fluid inlet.
A directly related object of the invention is that force for movement of the inlet flow deflector be provided by a powered actuated.
A further related object of the invention is that the inlet flow deflector, as a sum of its parts, extend over a majority of a width of the waterjet fluid inlet.
Yet one more object of the invention is that the instant invention waterjet propulsor can be a pressurized system waterjet.
The invention will be better understood upon reference to the drawings and detailed description of the invention which follow in which: